docs: def _raise_error_if_container_is_missing_an_utterance(self):
          """ Check if there is a dataset for every utterance in every container, otherwise raise an error. """
          expected_keys = frozenset(self.utt_ids)
  
          for cnt in self.containers:
              keys = set(cnt.keys())
  
              if not keys.issuperset(expected_keys):
                  raise ValueError('Container is missing data for some utterances!')